Definition Securuty

How can we add objects to read only access in definition security? I went to the definition security tool from application designer. Created the new group, added some application engine programs and saved. It did not ask anywhere about read only accesss in group. I opened permission list in File -> Open -> Permission list, added my group to that permission list and try to change display only option from 'NO' to yes. Its not changing. Please let me know how to change the display only option and where do we assign that permission list?